Abstract
The chemical composition of the essential oil from aerial parts of Minthostachys acris Schmidt-Leb. grown in Cuzco was studied. A total of 59 volatile compounds were identified by gas-chromatography-flame ionization detector and gas chromatography-mass spectrometry in the essential oil obtained by steam distillation, of which the most prominent were pulegone (54.4%), cis-menthone (11.0%), and thymol (6.3%).
The genus Minthostachys Griseb. (Lamiaceae) is found in middle elevations along the Andes, from Venezuela to Argentina. 1 This genus includes 17 species according to some authors. 2 The review of the literature shows that much research has been directed at Minthostachys verticillata and Minthostachys mollis that at any other species. 2 In particular, Minthostachys acris Schmidt-Leb. is an aromatic shrub, growing wild in the Cuzco area and used as seasoning, for treatment of diarrhea, colics, flatulence, stomach pain, bruises, and for pest protection of stored tubers. 2 Minthostachys acris is frequently treated as separate in Peruvian researches, but then erroneously called Minthostachys glabrescens (Benth.) Epling. 2 The unique report about the chemical composition of M. glabrescens essential oil found pulegone, menthone (or trans-menthone), and isomenthone (or cis-menthone) as the major components. 3 Therefore, the present study was done to analyze the chemical composition of the essential oil from aerial parts of M. acris Schmidt-Leb. grown in Cuzco.
A total of 59 volatile compounds were identified in the essential oil (99.8% of the total composition) (Table 1). A chemical study on the volatile oil from leaves of Peruvian M. acris species have been carried out, with the presence of 36 compounds, in which the main components were pulegone (45.3%), trans-menthone (17.8%), and cis-menthone (6.4%). 3 Results of this work showed a different pattern compared to those previously found, particularly that the trans-menthone/cis-menthone ratio is opposed. Information available on the essential oil composition for other Minthostachys species showed that M. mollis var. mandoniana (Briq.) Schmidt-Leb. from Bolivia contained high amounts of pulegone and menthone 4 and M. verticillata (Griseb.) Epling from Argentina was pulegone dominated. 5 Many studies show that the chemical composition of essential oils varies noticeably according to numerous factors, including environmental geobotanical conditions, cultivation technique, plant age, harvest period, among others. 6
Chemical Composition of Minthostachys acris Essential Oil.
LRIA and LRIP experimental linear retention indices on DB-5ms and HP-Innowax columns, trace (<0.1%). *tentatively identified compound by comparison with literature data.
Experimental
Materials and Isolation of Essential Oil
Leaves were collected in Julio 2011 from wild shrubs in the Cuzco region in southeast Peru (2941 m height above sea level). Voucher specimen (accession numbers 763 CUZ) was deposited at the herbarium of the National University of San Antonio Abad del Cusco. The sample (10 kg) from different plants was steam distilled in a metallic distillation apparatus coupled to a Clevenger-type collector. Oil yield was 0.21 % v/m.
Gas Chromatography
Analyses of the essential oil was performed by gas chromatography with a flame ionization detector (GC-FID) on a Konik 4000A (Konik, Barcelona) coupled to a 30 m × 0.25 mm di ×0.25 µm HP-5ms or HP-Innowax column under the experimental conditions: 60°C (2 min), 60°C to 220°C (4°C/min) and 220°C (5 min); helium flow rate at 1 mL/minutes; injector and detector temperature 240°C.
For GC-MS an Agilent 6890N (Santa Clara, CA, EE.UU.) coupled to a mass detector Agilent 5975B was used. The column and analytical conditions were the same as GC-FID. Compounds were identified using their linear retention indices and mass spectra. Linear retention indices, calculated using linear interpolation relative to retention times of C8-C24 of n-alkanes, were compared with those standards and data from the literature. 7 Mass spectra were compared with corresponding reference standard data 7 and mass spectra from NIST 05, Wiley 6, NBS 75 k and in-house Flavorlib libraries.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) declared no financial support for the research, authorship, and/or publication of this article.